Descriptive Text

Figure 2. Schematic of double grating monochromator and three optical sources selectable by a motorized mirror. Exit port of monochromator is in a light tight enclosure in which the exit port is imaged by mirrors onto a photodetector. Two orthogonal motorized stages can position the detector in the light beam. The stages are stages perpendicular to the optical axis (light beam). A rotating stage can position one of three detectors in the light beam. Only one position has the two motorized stages, the other two positions are stationary on the rotating stage. A shutter is placed at the monochromator exit port to block the light from the detectors. A baffle is placed in front of the detectors to block stray light. A beam splitter is positioned in the beam in front of the baffle to direct light to a monitor detector. A laser can also be selected as a source for alignment of the detectors.

Figure 3. Graph of the spectral responsivities of typical silicon (Si), indium gallium arsenide (InGaAs), and germanium (Ge) photodiodes.

Curve 1. UDT Sensors model UV-100 silicon photodiode absolute responsivity (in amperes per watt [A/W]) increases nearly linearly from 0.07 [A/W] at 200 nm to 0.27 [A/W] at 500 nm, with a small dip at 365 nm.

Curve 2. Hamamatsu model S1227-type silicon photodiode absolute responsivity (in amperes per watt [A/W]) increases nearly linearly from 0.10 [A/W] at 200 nm to a peak of 0.36 [A/W] around 720 nm, with small dips near 275 nm and 365 nm. The responsivity decreases smoothly from the 0.36 [A/W] peak near 720 nm to 0.07 [A/W] at 1000 nm and to less than 0.01 [A/W] at 1100 nm.

Curve 3. Hamamatsu model S1337-type silicon photodiode absolute responsivity (in amperes per watt [A/W]) increases nearly linearly from 0.10 [A/W] at 200 nm to a peak of 0.51 [A/W] around 970 nm, with small dips near 275 nm and 365 nm. The responsivity decreases smoothly from the 0.36 [A/W] peak near 720 nm to 0.07 [A/W] at 1000 nm and to less than 0.01 [A/W] at 1100 nm.

Curve 4. Absolute responsivity (in amperes per watt [A/W]) of a NIST-built, light-trapping photodetector using Hamamatsu model S1337-type silicon photodiode. The absolute responsivity increases linearly from 0.32 [A/W] at 405 nm to 0.74 [A/W] at 920 nm.

Curve 5. Indium gallium arsenide photodiode absolute responsivity (in amperes per watt [A/W]) rapidly increases from 0.08 [A/W] at 700 nm to about 0.66 [A/W] at 960 nm, then roughly linearly to about 1.04 [A/W] at 1600 nm, with several small dips in-between. The responsivity then decreases rapidly to 0.06 [A/W] at 1740 nm and to less than 0.01 [A/W] at 1800 nm.

Curve 6. EG&G Judson thermal-electrically cooled germanium photodiode absolute responsivity (in amperes per watt [A/W]) increases nearly linearly from 0.08 [A/W] at 700 nm to a peak of about 0.84 [A/W] around 1505 nm. The responsivity decreases smoothly from the peak to about 0.43 [A/W] at 1600 nm and 0.04 [A/W] at 1800 nm. Germanium photodiode temperature is -20 °C.

Uniformity plots

Hamamatsu model S1337-1010BQ silicon photodiode spatial responsivity at 500 nm. Photoactive area is square and has an area of one square centimeter. Responsivity is normalized to the center response. Responsivity changes by < 0.2 % over most of the central region of the photodiode. The responsivity increases from the center by 0.2 % about 3 mm from the center and by 0.6 % about 4 mm from the center.

Hamamatsu model S1337-1010BQ silicon photodiode spatial responsivity at 1000 nm. Photoactive area is square and has an area of one square centimeter. Responsivity is normalized to the center response. Responsivity changes by < 0.2 % over most of the central region of the photodiode. The lower left-hand corner has a peak and low points that vary by 0.4 %.

Hamamatsu model S2281 silicon photodiode spatial responsivity at 500 nm. Photoactive area is round and has an area of one square centimeter. Responsivity is normalized to the center response. Responsivity slopes down by 0.4 % from about 3 mm above the center to about 1 mm below center.

Hamamatsu model S2281 silicon photodiode spatial responsivity at 1000 nm. Photoactive area is round and has an area of one square centimeter. Responsivity is normalized to the center response. Responsivity slopes away from the center, decreasing by 0.2 % about 3  mm from the center.

UDT Sensors model UV100 silicon photodiode spatial responsivity at 350 nm. Photoactive area is round and has an area of one square centimeter. Responsivity is normalized to the center response. Responsivity slopes down by 0.6 % from about 3 mm to the right of the center to about 3 mm to the left of center.

EG&G Judson thermoelectrically cooled germanium photodiodes spatial responsivity at 1000 nm. Photoactive area is round and has an area of 20 square millimeters. Responsivity is normalized to the center response. Responsivity slopes down by 0.6 % from about 1 mm to the left of the center to about 1.5 mm to the right of center.

EG&G Judson thermoelectrically cooled germanium photodiodes spatial responsivity at 1500 nm. Photoactive area is round and has an area of 20 square millimeters. Responsivity is normalized to the center response. Responsivity slopes down by 0.4 % from about 1 mm above the center to about 1 mm below center.

EG&G Judson thermoelectrically cooled germanium photodiodes spatial responsivity at 1600 nm. Photoactive area is round and has an area of 20 square millimeters. Responsivity is normalized to the center response. Responsivity slopes down by 2 % from about 1.5 mm below the center to about 1.5 mm above center.

Figure 4. Graph of the relative expanded uncertainty for measurements with three different working standard types.

Curve 1. UV silicon photodiode working standards: maximum at 200 nm of 3.8 %, from 205 nm to 400 nm fluctuates between 1 % and 2 %, and from 405 nm to 500 nm fluctuates between 0.4 % and 0.8 %. Measurements at power levels less than 20 µW.

Curve 2. Visible to Near Infrared silicon photodiode working standards: from 350 nm to 400 nm decreases from 3 % to 1.6 %, from 405 nm to 435 nm decreases from 0.4 % to 0.3 %, from 440 nm to 920 nm constant at 0.2 %. The uncertainty increases sharply at 925 nm to 2.8  % and fluctuates between 1.6 % and 4.4 % to 1100 nm. Measurements at power levels less than 1 µW.

Curve 3. Near Infrared indium gallium arsenide photodiode working standards: from 700 nm to 920 nm almost constant at 0.5 %, from 925 nm to 1600 nm fluctuates between 0.8 % to 1.6 %, from 1605 nm to 1800 nm increases to about 4 %. Measurements at power levels less than 1 µW.

Figure 5. Graph of relative expanded uncertainty for typical (200 nm and above) and Special Test 39080S (extended range to 193 nm) UV measurements.

Curve 1. Typical UV measurements: maximum at 200 nm of 3.8 %, from 205  nm to 215 nm decreases from 2 % to 1 % and is 1 % at 220 nm. Measurements at power levels less than 20 µW.

Curve 2. Extended range UV measurements: maximum at 193 nm of 5 %, decreasing to about 1 % at 200 nm, then remaining around 1 % to 210 nm. Measurements at power levels less than 20 µW.

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Online: March 2001   -   Last updated: October 2004